This invention relates to coated polycarbonate articles. More particularly, the invention relates to polycarbonate articles coated with abrasion and chemical resistant protective coatings, which are flexible and thermoformable.
Thermoplastics, such as polycarbonates, polyesters, polystyrene, polyvinyl, polymethacrylates and the like are commercially important materials, which are useful in a wide range of applications, from non-opaque, impact resistant sheets to shaped articles. Many of these materials have rather low resistance to scratching and abrasion and are susceptible to attack by common solvents and chemicals. In addition, these polymers often undergo degradation upon exposure to ultraviolet light.
These problems have largely been overcome by coating the thermoplastic materials with hard, abrasion and chemical resistant coatings. Such coatings may contain an ultraviolet light-absorbing compound to protect the thermoplastic against the deleterious effects of ultraviolet light. Typically, these coatings have been radiation-curable, acrylate-based coatings.
Previous attempts to produce hard, abrasion and chemical resistant coatings have generally employed highly functionalized acrylic monomers. The resulting cured coatings were highly crosslinked. Moore et al, in U.S. Pat. No. 4,198,465, describe a polycarbonate article coated with a durably adherent mar, abrasion and chemical resistant UV-cured coating. The coating is comprised of the photoreaction products of polyfunctional acrylate monomers and resorcinol monobenzoate.
Although crosslinked acrylic coatings are quite hard and resist scratching and abrasion, they are often rather brittle and are substantially thermoset. These properties can be disadvantageous if the coated thermoplastic is to be thermoformed or is to be employed in applications where flexing will be encountered. Attempts to flex or thermoform sheets or films coated with highly crosslinked coatings may result in rupture or separation of the coating, because the coating lacks the requisite elongation characteristics.
Various post-formable coating compositions have been proposed. For example, Moore et al., in U.S. Pat. No. 4,107,391, describe thermoformable coatings for thermoplastic substrates. These coatings are photopolymerizable wax-containing resins or blends which comprise solutions of either unsaturated polyesters or polymethylmethacrylate in styrene or methylmethacrylate.
A. F. Leo, in U.S. Pat. No. 4,561,950, discloses post-formable coatings for metallic substrates, which comprise a silicone dicarbinol diurethane diacrylate, isobornyl acrylate or methacrylate, acrylic acid or methacrylic acid and optionally an aliphatic polyester urethane diacrylate, wherein the polyester has a molecular weight in the range of 600 to 2000. These coatings are said to be radiation polymerizable and flexible in the cured state.
U.S. Pat. No. 4,507,198, Y. C. Chu, discloses UV-curable coating compositions for floor tiles and other applications. These coatings contain an acrylate-terminated urethane-polyester oligomer and a mono-functional acrylate diluent which is the reaction product of a hydroxyalkyl acrylate and an isocyanate.
A need continues to exist for abrasion and chemical resistant coated thermoplastic articles which are both thermoformable and flexible.